2 Answers
2

The short answer is that those two graphs are consistent with each other. The first shows a 33 year trend of declining Arctic sea ice (summer minimum, I think), whereas the second highlights inter-annual variation in Arctic sea ice over the last four years. We don't expect long-term trends to be strictly monotonic increases or decreases, so both positive or negative year-on-year differences, such as those between 2012 and 2013, can be consistent with the trend.

Few things to notice are that while the Arctic Sea volume increased 50%, the volume increase was marginal compared with the volume of sea ice in 1979. Next, if you review the graph below, one year spikes are not that unusual, though if there was another 50% the volume increase from 2013 to 2014, it would be of note, given the rarity of significant year over year increases in Arctic Sea volume.